The present invention relates to a fuel cell apparatus which combines an insulating and a heat exchanging function.
Solid oxide fuel cells operate at high temperature and typically have a “hot box” or “hot zone” which houses the fuel cell stacks, reforming apparatus, heat exchangers and other equipment that need to be at the operating temperature of the fuel cells. This hot box is insulated to reduce energy losses and to prevent thermal shocks to the fuel cell stacks. Usually, this insulation consists of thick blankets of alumina fibers, or asbestos. This is undesirable from a health perspective, as the blankets must be handled carefully to prevent the release of fibers of the insulating material, as these fibers can be hazardous or carcinogenic. In addition, the protective equipment required to be worn by workers handling this material is expensive and cumbersome.
Thick insulating blankets are undesirable for a potential consumer product, as they occupy a large amount of space, and the product packaging should be as small as possible, especially for transportation applications. Further, incorporating heat exchangers and other devices inside the hot box area necessitates a larger hot box. This has a larger surface area and therefore more thermal loss than a smaller hot box, which impairs efficiency.
Additionally, the use of insulating blankets does not permit convenient control of the stack or hot zone temperature as the insulation is constant and not variable. It may be desirable to increase or decrease the insulation around the hot zone to regulate the stack temperature in a stack control system. It may be further desirable to include a method of cooling the stack as part of the stack control system.
Therefore there is a need in the art to overcome the difficulties of the prior art, and provide a system that may allow the hot box to be made smaller and which may permit cooling of the stack and/or a variable insulating effect.